In the manufacture of semiconductor devices, ion implantation is often used to dope semiconductor workpieces (e.g., silicon wafers) with impurities. For example, ion implanters or ion implantation systems may treat a workpiece with an ion beam, to produce n-type or p-type doped regions or to form passivation layers on the workpiece. When used for doping semiconductors, the ion implantation system injects a selected ion species to produce the desired extrinsic material.
Typically, ion beam implanters comprise an ion source configured to generate positively charged ions from ionizable source material. An ion beam is formed from the generated ions and is directed along a beam path to an ion implantation station. The ion implanter may comprise beam forming and shaping structures (e.g., beam corrector magnets) extending between the ion source and the implantation station. The beam forming and shaping structures maintain the integrity of the ion beam en route to the implantation station.
Since the size of a workpiece is often greater than the size of an ion beam, hybrid scan ion implanters are often employed to enable an ion beam to scan over a surface of a workpiece. In general, a scanning system may comprise a pair of scan plates (or a scanning electromagnet for electromagnetic scanning) positioned to deflect an ion beam and a scan waveform generator configured to apply voltages, associated with a scan waveform, to the scan plates (or to apply currents to the scanning electromagnet for electromagnetic scanning). The voltages produce a time varying electric or magnetic field between the plates to deflect or scan a beam (e.g., a pencil beam) back and forth over a scan path (e.g., into a ribbon beam), thereby effectively spreading out a beam, while moving a workpiece in an orthogonal direction.
Often, it is desirable to provide uniform implantation over the surface of a workpiece. Unfortunately, in practical application an ion implantation system is often subject to non-uniformities over a wafer. If these non-uniformities are not corrected the workpiece may be implanted non-uniformly and product yield may suffer.